Serum antibody and cellular responses in LEW and F344 rats after immunization with Mycoplasma pulmonis antigens

Regulatory CD4+CD25+ T Cells Dampen Inflammatory Disease in Murine Mycoplasma Pneumonia and Promote IL-17 and IFN-γ Responses

Mycoplasmas cause respiratory diseases characterized by persistent infection and chronic airway inflammation. Mycoplasma lung disease is immunopathologic, with CD4⁺ Th cells determining both disease severity and resistance to infection. Th2 cell responses promote immunopathology, while Th1 cells confer resistance to infection. However, regulatory CD4⁺ T cells may also have a role in the pathogenesis of mycoplasma respiratory diseases. We hypothesized Treg cells control the severity of the inflammatory lesions and may also promote persistence of infection. To examine this, BALB/c mice were depleted of CD25⁺ cells, and had increased disease severity due to Mycoplasma pulmonis infection. Increases in mycoplasma antibody responses and lymphocyte infiltration into lungs also occurred after CD25⁺ cell depletion. CD4⁺CD25⁺ regulatory T cells promoted IFN-γ and IL-17 mycoplasma-specific CD4⁺ T cell responses in vitro and in vivo, while dampening IL-13⁺ Th responses. Neither IL-10 nor TGF-ß expression was detected in CD4⁺CD25⁺ T cells from lymph nodes. Thus, a regulatory T cell population plays an important role in controlling damaging immune responses in mycoplasma respiratory disease but does not contribute to persistence of infection. It appears that a regulatory T cell population preferentially dampens Th2 cell-mediated inflammatory responses to mycoplasma through a mechanism independent of IL-10 or TGF-ß characteristic of “classic” Treg cells.

Antigen-pulsed bone marrow-derived and pulmonary dendritic cells promote Th2 cell responses and immunopathology in lungs during the pathogenesis of murine Mycoplasma pneumonia

Mycoplasmas are a common cause of pneumonia in humans and animals, and attempts to create vaccines have not only failed to generate protective host responses, but they have exacerbated the disease. Mycoplasma pulmonis causes a chronic inflammatory lung disease resulting from a persistent infection, similar to other mycoplasma respiratory diseases. Using this model, Th1 subsets promote resistance to mycoplasma disease and infection, whereas Th2 responses contribute to immunopathology. The purpose of the present study was to evaluate the capacity of cytokine-differentiated dendritic cell (DC) populations to influence the generation of protective and/or pathologic immune responses during M. pulmonis respiratory disease in BALB/c mice. We hypothesized that intratracheal inoculation of mycoplasma Ag-pulsed bone marrow-derived DCs could result in the generation of protective T cell responses during mycoplasma infection. However, intratracheal inoculation (priming) of mice with Ag-pulsed DCs resulted in enhanced pathology in the recipient mice when challenged with mycoplasma. Inoculation of immunodeficient SCID mice with Ag-pulsed DCs demonstrated that this effect was dependent on lymphocyte responses. Similar results were observed when mice were primed with Ag-pulsed pulmonary, but not splenic, DCs. Lymphocytes generated in uninfected mice after the transfer of either Ag-pulsed bone marrow-derived DCs or pulmonary DCs were shown to be IL-13(+) Th2 cells, known to be associated with immunopathology. Thus, resident pulmonary DCs most likely promote the development of immunopathology in mycoplasma disease through the generation of mycoplasma-specific Th2 responses. Vaccination strategies that disrupt or bypass this process could potentially result in a more effective vaccination.

Dendritic cells are the major antigen presenting cells in inflammatory lesions of murine Mycoplasma respiratory disease

Mycoplasmas cause chronic respiratory diseases in animals and humans, and to date, development of vaccines have been problematic. Using a murine model of mycoplasma pneumonia, lymphocyte responses, specifically T cells, were shown to confer protection as well as promote immunopathology in mycoplasma disease. Because T cells play such a critical role, it is important to define the role of antigen presenting cells (APC) as these cells may influence either exacerbation of mycoplasma disease pathogenesis or enhancement of protective immunity. The roles of APC, such as dendritic cells and/or macrophages, and their ability to modulate adaptive immunity in mycoplasma disease are currently unknown. Therefore, the purpose of this study was to identify individual pulmonary APC populations that may contribute to the activation of T cell responses during mycoplasma disease pathogenesis. The present study indeed demonstrates increasing numbers of CD11c⁻ F4/80⁺ cells, which contain macrophages, and more mature/activated CD11c⁺ F4/80⁻ cells, containing DC, in the lungs after infection. CD11c⁻ F4/80⁺ macrophage-enriched cells and CD11c⁺ F4/80⁻ dendritic cell-enriched populations showed different patterns of cytokine mRNA expression, supporting the idea that these cells have different impacts on immunity in response to infection. In fact, DC containing CD11c⁺ F4/80⁻ cell populations from the lungs of infected mice were most capable of stimulating mycoplasma-specific CD4⁺ Th cell responses in vitro. In vivo, these CD11c⁺F4/80⁻ cells were co-localized with CD4⁺ Th cells in inflammatory infiltrates in the lungs of mycoplasma-infected mice. Thus, CD11c⁺F4/80⁻ dendritic cells appear to be the major APC population responsible for pulmonary T cell stimulation in mycoplasma-infected mice, and these dendritic cells likely contribute to responses impacting disease pathogenesis.

Interferon gamma and interleukin 4 have contrasting effects on immunopathology and the development of protective adaptive immunity against mycoplasma respiratory disease

For vaccine development, it is critical to understand the regulatory mechanisms determining resistance and immunopathology against mycoplasma respiratory diseases. The present study evaluated the contribution of the polarizing cytokines interferon gamma (IFN-gamma) and interleukin 4 (IL-4) in the regulation of mycoplasma-specific immunity. The absence of a single cytokine (either IFN-gamma or IL-4) uniquely altered the expression of multiple chemokines and cytokines in the lungs of uninfected mice and influenced responses to mycoplasma infection. Most importantly, prior nasal-pulmonary immunization of IFN-gamma(-/-) mice led to exacerbated mycoplasma disease, whereas immunized IL-4(-/-) mice were dramatically more resistant than wild-type mice. Helper T cell type 2 responses in IFN-gamma(-/-) mice corresponded to immunopathologic reactions that developed after mycoplasma infection or immunization. Thus, adaptive immunity clearly can independently promote either protection or immunopathology against mycoplasma infection, and optimal vaccination appears to be dependent on promoting protective IFN-gamma-dependent networks (perhaps helper T cell type 1 responses) while minimizing the effect of IL-4-mediated responses, which dampen the generation of protective immunity.

NK cells interfere with the generation of resistance against mycoplasma respiratory infection following nasal-pulmonary immunization

The purpose of the present study was to determine the impact of NK cells on the development of protective adaptive immunity in response to nasal-pulmonary immunization against mycoplasma. Depletion of NK cells before nasal-pulmonary immunization enhanced resistance to mycoplasma respiratory infection. The effect of NK cells on the generation of protective immunity in lungs was dependent on lymphoid cells, as immunization of either SCID mice or immunocompetent mice depleted of CD4(+) T cells did not demonstrate any increased resistance in the presence or absence of NK cells. The presence of NK cells at the time of nasal-pulmonary immunization modulated mycoplasma-specific cytokine responses in lungs and lower respiratory nodes. In particular, NK cells skewed the mycoplasma-specific T cell cytokine responses in the draining lymph nodes to higher IL-4, IL-13, and IL-17 while lowering IFN-gamma responses. Adoptive transfer of total lung lymphocytes isolated from immunized mice into naive mice led to a significant reduction in the mycoplasma numbers in lungs, and the resistance was greater if cells were obtained from immunized mice that were depleted of NK cells. Similar results were obtained if purified B cells, T cells, or CD4(+) T cells were used. Interestingly, this is the first time that a favorable role of functional CD4(+) T cells in mediating protection in mycoplasma respiratory disease was demonstrated. Thus, NK cells can influence the responses of multiple lymphocyte populations capable of mediating resistance to mycoplasma infection.

A novel IL-17-dependent mechanism of cross protection: respiratory infection with mycoplasma protects against a secondary listeria infection

Immune responses to pathogens occur within the context of current and previous infections. Cross protection refers to the phenomena where infection with a particular pathogen provides enhanced resistance to a subsequent unrelated pathogen in an antigen-independent manner. Proposed mechanisms of antigen-independent cross protection have involved the secretion of IFN-gamma, which activates macrophages, thus providing enhanced innate immunity against the secondary viral or bacterial pathogen. Here we provide evidence that a primary infection with the chronic respiratory pathogen, Mycoplasma pulmonis, provides a novel form of cross protection against a secondary infection with Listeria monocytogenes that is not mediated by IFN-gamma, but instead relies upon IL-17 and mobilization of neutrophils. Mice infected with M. pulmonis have enhanced clearance of L. monocytogenes from the spleen and liver, which is associated with increased numbers of Gr-1(+)CD11b(+) cells and higher levels of IL-17. This enhanced clearance of L. monocytogenes was absent in mice depleted of Gr-1(+) cells or in mice deficient in the IL-17 receptor. Additionally, both the IL-17 receptor and neutrophils were essential for optimal clearance of M. pulmonis. Thus, a natural component of the immune response directed against M. pulmonis was able to enhance clearance of L. monocytogenes.

THE MULTIFACETED ROLE OF T CELL-MEDIATED IMMUNITY IN PATHOGENESIS AND RESISTANCE TO MYCOPLASMA RESPIRATORY DISEASE

Mycoplasma respiratory diseases have a significant impact on the economy, health and wildlife. The hallmark of these diseases is the persistence of the mycoplasma infections and chronic inflammatory responses associated with the airways. There is still much that needs to be understood about the immune mechanisms involved in mycoplasma disease and resistance from infection. It is clear that immune responses can contribute to the generation of inflammatory lesions in mycoplasma respiratory disease, as well as provide protection from infection and extrapulmonary dissemination of the organisms. The evolution of this lung disease is under the control innate immune mechanisms and the contrasting effects of different T cell populations. The mechanisms of immunity involved in mycoplasma diseases are multifaceted, and a fascinating story of its complexity is being uncovered. Research in mycoplasma respiratory diseases have underscored the idea that immunity along the respiratory tract against infectious agents is a dynamic process and involves a network of cellular and cytokine signals that determine the type of responses generated, and ultimately, the outcome of infection. The aim of this article is to present on overview of our work on mycoplasma disease and immunity, focusing on the interactions and regulation of T cell responses that influence disease pathogenesis. We will first provide an overview of immune mechanisms involved in controlling infection and participate in the generation of T cell responses, and the role of T cell populations in generating protection and contributing to lesion development will be discussed.

T-bet deficiency facilitates airway colonization by Mycoplasma pulmonis in a murine model of asthma

Epidemiological and clinical evidence suggest a correlation between asthma and infection with atypical bacterial respiratory pathogens. However, the cellular and molecular underpinnings of this correlation remain unclear. Using the T-bet-deficient (T-bet(-/-)) murine model of asthma and the natural murine pathogen Mycoplasma pulmonis, we provide a mechanistic explanation for this correlation. In this study, we demonstrate the capacity of asthmatic airways to facilitate colonization by M. pulmonis and the capacity of M. pulmonis to exacerbate symptoms associated with acute and chronic asthma. This mutual synergism results from an inability of T-bet(-/-) mice to mount an effective immune defense against respiratory infection through release of IFN-gamma and the ability of M. pulmonis to trigger the production of Th2-type cytokines (e.g., IL-4 and IL-5), and Abs (e.g., IgG1, IgE, and IgA), eosinophilia, airway remodeling, and hyperresponsiveness; all pathophysiological hallmarks of asthma. The capacity of respiratory pathogens such as Mycoplasma spp. to dramatically augment the pathological changes associated with asthma likely explains their association with acute asthmatic episodes in juvenile patients and with adult chronic asthmatics, >50% of whom are found to be PCR positive for M. pneumoniae. In conclusion, our study demonstrates that in mice genetically predisposed to asthma, M. pulmonis infection elicits an inflammatory milieu in the lungs that skews the immune response toward the Th2-type, thus exacerbating the pathophysiological changes associated with asthma. For its part, airways exhibiting an asthmatic phenotype provide a fertile environment that promotes colonization by Mycoplasma spp. and one which is ill-equipped to kill and clear respiratory pathogens.

Depletion of CD8+ T cells exacerbates CD4+ Th cell-associated inflammatory lesions during murine mycoplasma respiratory disease

Mycoplasma infection is a leading cause of pneumonia worldwide and can lead to other respiratory complications. A component of mycoplasma respiratory diseases is immunopathologic, suggesting that lymphocyte activation is a key event in the progression of these chronic inflammatory diseases. The present study delineates the changes in T cell populations and their activation after mycoplasma infection and determines their association with the pathogenesis of murine Mycoplasma respiratory disease, due to Mycoplasma pulmonis infection. Increases in T cell population numbers in lungs and lower respiratory lymph nodes were associated with the development of mycoplasma respiratory disease. Although both pulmonary Th and CD8(+) T cells increased after mycoplasma infection, there was a preferential expansion of Th cells. Mycoplasma-specific Th2 responses were dominant in lower respiratory lymph nodes, while Th1 responses predominated in spleen. However, both mycoplasma-specific Th1 and Th2 cytokine (IL-4 and IFN-gamma) responses were present in the lungs, with Th1 cell activation as a major component of the pulmonary Th cell response. Although a smaller component of the T cell response, mycoplasma-specific CD8(+) T cells were also a significant component of pulmonary lymphoid responses. In vivo depletion of CD8(+) T cells resulted in dramatically more severe pulmonary disease, while depletion of CD4(+) T cells reduced its severity, but there was no change in mycoplasma numbers in lungs after cell depletion. Thus, mycoplasma-specific Th1 and CD8(+) T cell activation in the lung plays a critical regulatory role in development of immunopathologic reactions in Mycoplasma respiratory disease.

Gender is a major factor in determining the severity of mycoplasma respiratory disease in mice

Gender is a significant factor in determining the susceptibility to and severity of pulmonary diseases in both humans and animals. Murine respiratory mycoplasmosis (MRM), due to Mycoplasma pulmonis infection, is an excellent animal model for evaluation of the role of various host factors on the development of acute or chronic inflammatory lung diseases. MRM has many similarities to mycoplasma respiratory disease in humans. The purpose of the present study was to determine whether gender has a significant impact on lung disease due to M. pulmonis infection in mice. It was demonstrated that male mice consistently developed more severe disease in the lung parenchyma than did female mice. There was no gender difference in disease severity along the airways or any difference in mycoplasma numbers in lungs of male and female mice. Furthermore, surgical removal of reproductive organs reduced the severity of mycoplasma disease and the numbers of mycoplasma organisms recovered from lungs. Thus, gender plays a significant role in determining the severity of M. pulmonis disease. In fact, the gender of the host was a major factor in determining whether an acute or chronic inflammatory lung disease developed after infection with M. pulmonis.

Pathogenicity of cilia-associated respiratory (CAR) bacillus isolates for F344, LEW, and SD rats

We conducted experiments to test whether rats of F344, LEW, and SD strains differ in susceptibility to mycoplasma-free isolates of cilia-associated respiratory (CAR) bacillus, whether Mycoplasma pulmonis can affect expression of CAR bacillus disease, and whether isolates of CAR bacillus differ in virulence for rats. In the first experiment, 24 rats of each strain were inoculated intranasally with 10(7) bacilli of CAR bacillus X1428D/AS, and 24 rats of each strain were inoculated with sterile medium (controls). Eight weeks later, eight inoculated rats and eight control rats of each strain were euthanatized, eight inoculated and eight control rats were given 10(6.5) colony-forming units of M. pulmonis X1428D, and eight inoculated rats and eight control rats were sham inoculated. Four rats of each group were euthanatized 4 or 8 weeks after the second inoculation. Severity of lesions in nasal passages, middle ear, trachea, and lungs was assessed by scoring. Rats of all three strains given CAR bacillus had typical lesions of similar severity; M. pulmonis X1428D was avirulent and did not exacerbate CAR bacillus disease. In the second experiment, groups of eight rats of F344 and SD strains were given 10(5) or 10(7) CAR bacillus X1328E, X1428D/AS, or X2450D and euthanatized 8 or 16 weeks later. Isolates X1428D/AS and X2450D caused similar lesions in rats of both strains and at both doses, but CAR bacillus X1328E was avirulent. Rats of the tested strains are similarly susceptible to CAR bacillus disease, but CAR bacillus isolates differ in virulence.

Chronic respiratory mycoplasmosis in C3H/HeN and C57BL/6N mice: lesion severity and antibody response

Mycoplasma pneumoniae is a leading, worldwide cause of death and disability due to pneumonia. Mycoplasma pulmonis infection in mice is an invaluable model for the study of host defenses against respiratory mycoplasmas in vivo. C3H/HeN mice are much more susceptible to acute inflammatory lung disease due to M. pulmonis than C57BL/6N mice, but little is known about the chronic disease in these mouse strains. We infected C3H/HeN and C57BL/6N mice with 10(4) CFU of M. pulmonis UAB CT and evaluated them at weekly intervals by quantitative mycoplasma culture of nasal passages, trachea, and lungs, assessment of lesion severity in nasal passages, trachea, and lungs, and determination of serum immunoglobulin classes and subclasses by enzyme-linked immunosorbent assay. We found that C3H/HeN mice had 2 to 5 logs more organisms in their lungs and far more severe lung disease than C57BL/6N mice through 63 days postinfection. Although both strains of mice developed the same classes of antibody, C3H/HeN mice had much greater anti-M. pulmonis immunoglobulin G (IgG) responses in the IgG1 and IgG2a subclasses than C57BL/6N mice. These results suggest that adaptive immunity does not effect resolution of chronic mycoplasma infection and disease in the lungs.

Impact of experimental genital mycoplasmosis on pregnancy outcome in Sprague-Dawley rats

Specific-pathogen-free (SPF) female Sprague-Dawley rats were infected by intravaginal inoculation with 3 x 10(7) CFU of Mycoplasma pulmonis X1048 in 0.1 ml of Frey's broth or with an equal volume of sterile Frey's broth. A minimum of 10 days postinfection, rats were bred to noninfected males. Rats were necropsied at days 11, 14, and 18 of gestation and within 24 h of parturition. Throughout pregnancy, at least 50% of rats remained infected in the lower genital tract. At parturition, the major site of colonization was the respiratory tract (P = 0.02). M. pulmonis was not isolated from any site of any control rat. Pregnancy outcome was adversely affected by infection with M. pulmonis. Infected rats had significantly smaller litter sizes at day 18 of gestation (P < or = 0.01) and at term (P < or = 0.004). No statistically significant differences among the gestational stages in infected rats were noted for litter size. Total litter weight is a reflection of individual pup weight and of the number of pups born. Therefore, it was obvious that infected rats would have a significantly lower (P < or = 0.008) total litter weight than noninfected controls. However, when individual pup weights were considered, infected pups (n = 49) also had significantly lower (P < or = 0.0001) birth weights than did noninfected controls (n = 68). The incidence of an adverse pregnancy outcome at term (stillbirths, macerated fetuses, or resorptions) was higher (P < or = 0.01) in infected rats than in noninfected control rats. No stillborn pups or macerated fetuses were observed in any control term rats (n = 5). All control rats had live-born pups. Three infected rats had no live-born offspring. Resorptions were more common in infected rats than in control rats (P < or = 0.01). The mean number of resorptions per rat was greater in rats which went to term than in rats necropsied during gestation, indicating that the severity of disease was progressive. The rat is frequently the laboratory animal of choice for a wide variety of reproductive studies, and the experimental parameters that are most often measured (litter size, pup weight, and neonatal survival) were all adversely affected by genital mycoplasmosis. Genital mycoplasmosis is important as an animal model for the interaction of infectious agents and the host during pregnancy as well as in its own right as a confounding variable affecting research projects which use the rat as a model to study reproductive function and physiology.

Effects of aging on exocrine immune responses to Mycoplasma pulmonis

Formalinized Mycoplasma pulmonis was used to immunize 3 different age groups of Fischer 344 rats. A specific antibody to this antigen was detected in both saliva and lung lavage fluids and differences were noted in the elicitation of secretory antibody between the different ages of the animals. Few statistical differences were noted between the three age groups for salivary IgG responses to M. pulmonis, regardless of the dosage given, even though all responses were greater than their respective control groups. The principal differences among the three age groups were noted in the kinetics of the response, that is, the amount of time that was necessary to produce a peak response. The younger group of animals took less time to produce a peak response than the older two groups, even though the magnitude of the response was lower. Salivary IgA responses to M. pulmonis appeared predominantly as a primary response, particularly in the senescent animals. Secondary salivary IgA responses were not significantly greater than their respective primary responses, suggesting that secretory IgA did not display classic anamnestic responses that were observed with salivary IgG. As with IgG responses, the senescent animals took longer to produce a peak salivary IgA response when compared to the other age groups. Lung lavage IgG responses, normalized to total protein, were greatest in the youngest group of animals and appeared to diminish as the age of the animal increased. In contrast, lung lavage IgA responses to M. pulmonis were of a greater magnitude in the senescent animals. These studies suggest that senescent animals are capable of eliciting a humoral immune response in mucosal secretions to Mycoplasma pulmonis. However, differences noted with regard to disease severity and mortality to respiratory mycoplasmosis in senescent animals may result from intrinsic defects in the quality of the humoral response or as a consequence of deficient cellular responses to this pathogen.

Brown Norway rats are high responders to bronchiolitis, pneumonia, and bronchiolar mastocytosis induced by parainfluenza virus

The pathogenesis of parainfluenza 1 (Sendai) virus infection was compared among 25-day-old BN, F344, and LEW rats to identify a sensitive as well as a resistant inbred rat strain to Sendai virus-induced lung injury during early life. At 7 days after inoculation, BN rats had 65-fold higher (P less than .001) pulmonary viral titers and threefold higher (P less than .002) numbers of neutrophils in bronchoalveolar lavage fluid than did F344 rats. At 14 days after inoculation, when most virus-induced inflammation had been resolved, BN rats had a threefold greater (P less than .01) incidence of bronchioles with aggregates of lymphocytes and macrophages than did F344 rats. Control BN rats had higher numbers of bronchiolar eosinophils than did F344 or LEW rats. Although viral inoculation resulted in increased numbers of bronchiolar mast cells in all three strains at 14 days, bronchiolar mast cell density was greater (P less than .005) in virus-inoculated BN and LEW rats than in F344 rats. We conclude that BN rats are high responders and F344 rats are low responders to Sendai virus-induced bronchiolitis, pneumonia, and airway mastocytosis. These strain differences may be useful in elucidating important pathogenetic mechanisms in virus-induced airway injury and mastocytosis.

Specific and nonspecific antibody responses in different segments of the respiratory tract in rats infected with Mycoplasma pulmonis

Murine respiratory mycoplasmosis resulting from Mycoplasma pulmonis infection in rats provides a useful model for the study of immunological and inflammatory mechanisms operative in the respiratory tract. We have previously shown that LEW rats develop more severe disease than do F344 rats. To further study the production of antibody responses in chronic respiratory disease due to M. pulmonis infection, we examined the distribution and development of M. pulmonis-specific antibody-forming cells (AFC) in different segments of the respiratory tracts of infected LEW and F344 rats. In these studies, the upper respiratory nodes were the initial site of antibody production after infection and remained the major site for recovery of AFC. Since infected LEW rats had equal or higher numbers of AFC than did infected F344 rats, these results suggest that the level of local antibody production alone is not responsible for the decreased susceptibility of F344 rats to murine respiratory mycoplasmosis. The differences in total antibody responses appear to be due to the greater numbers of cells recovered from the tissues of infected LEW rats compared with those recovered from F344 rats, suggesting that LEW rats may have greater production of chemotactic factors. Also, we demonstrate that nonspecific activation and/or recruitment of B cells occurs in the respiratory tracts of both LEW and F344 rats after infection with M. pulmonis.

Immunoglobulin class- and subclass-specific responses to Mycoplasma pulmonis in sera and secretions of naturally infected Sprague-Dawley female rats

Mycoplasma pulmonis causes chronic murine respiratory mycoplasmosis and genital disease in rats. Specific immunoglobulin M (IgM), IgA, and IgG and its subclasses present in sera and tracheal and uterine lavage samples from 36 naturally infected Sprague-Dawley female rats were tested for reactivity with M. pulmonis in an enzyme-linked immunosorbent assay. Ten specific-pathogen-free Sprague-Dawley female rats served as the negative controls. Tracheal and uterine lavage samples were cultured quantitatively for M. pulmonis. M. pulmonis was isolated from the trachea (35 of 36) and uterus (17 of 36) of naturally infected rats; all rats were infected in at least one of the two sites cultured. M. pulmonis was not isolated from any control rat. There was a significant difference in levels of specific antibody of all classes except IgG2c between control and naturally infected animals (P less than 0.001 for IgM, IgG, IgG1, and IgG2a; P less than 0.002 for IgG2b; and P less than 0.02 for IgA). There was no correlation between numbers of M. pulmonis cells isolated and the amount or class of antibody measured in serum or tracheal lavage specimens. The predominant antibodies to M. pulmonis found in the sera of naturally infected rats were IgG and IgM. The IgG2a subclass was responsible for the majority of IgG-positive animals. There were no differences between rats which were positive by culture for M. pulmonis in the uterus (U+) and rats which were negative by culture for M. pulmonis in the uterus (U-) with respect to distribution or amount of antibody classes and subclasses in the serum. However, tracheal wash samples from U+ rats had significantly higher (P less than 0.03) levels of specific IgG1 and IgG2a than those from U- rats. Conversely, IgG2a was present in higher levels in pooled uterine lavage specimens from U- rats than in those from U+ rats.

Alterations in lung prostaglandin synthesis and release in murine respiratory mycoplasmosis

Pathogenetic mechanisms in murine respiratory mycoplasmosis are poorly understood; however, non-specific immune responses appear to be important in controlling the growth of Mycoplasma pulmonis in vitro. To date, no study has examined the role of pulmonary prostaglandin production during the development of M. pulmonis infection. The present study was designed to determine if alterations in pulmonary prostaglandin synthesis and release occur in M. pulmonis infection and the possible role for prostaglandins in the modulation/pathogenesis of murine respiratory mycoplasmosis. Ten to 20 days after intranasal inoculation of pathogen-fee F344 rats with M. pulmonis, lung lavage concentrations of prostaglandin E (PGE) and thromboxane A2 (TxA2) were significantly elevated. To confirm a role for prostaglandins in the pathogenesis of murine mycoplasmosis we blocked the cyclo-oxygenase pathway with indomethacin. Indomethacin-treated rats had significantly lower lavage levels of PGE and TxA2 and significantly increased numbers of M. pulmonis in the lung. These data indicate that prostaglandins may be involved in the pathogenesis of murine respiratory mycoplasmosis, possibly through alteration of mycoplasmacidal and/or mycoplasmastatic mechanisms.

Interactions between mycoplasmas and the immune system

Mycoplasmas are a heterogenous group of prokaryotic organisms causing a wide variety of diseases, including autoimmune disorders. Thus, it is not surprising that various mycoplasmas strains, including Mycoplasma arginini, M. arthritidis, M. neurolyticum and M. pulmonis, are able to regulate the immune response. Though some of the studies of the immunomodulatory action of mycoplasmas have been done in vivo, the majority of the investigations have been conducted in vitro. This has led to the recognition that mycoplasmas are polyclonal activators of both B and T cells from several species, acting through MHC-restricted or -unrestricted pathways. Mycoplasma activation not only induces T-cell proliferation but also leads but to the formation of cytotoxic T cells. We, as well as others, have shown that mycoplasma-mediated B-cell activation induces proliferation as well as Ig secretion, and also that mycoplasma stimulation of lymphocytes may result in the production of cytokines. We communicate here our investigations into the effects of an M. arginini strain on the growth and maturation of preactivated B cells. After an initial biological characterization of the M. arginini effects in vitro, we established the protein nature of the growth-supporting activity and proceeded further on to isolate and identify the responsible proteins. The use of lipid- and lipoglycan-free extracts has allowed us to further extend our studies on the biological activities of the proteins from M. arginini and to compare these results with the effects obtained using live organisms. Furthermore, the study was extended to include a characterization of the in vivo-induced effects of live M. arginini. Altogether, the results from these experiments allow us to conclude that M. arginini is a T-cell independent polyclonal B-cell mitogen, mediated by five identified proteins, inducing growth and Ig secretion of both resting and preactivated B cells.

Serum antibody does not account for differences in the severity of chronic respiratory disease caused by Mycoplasma pulmonis in LEW and F344 rats

Chronic respiratory disease in rats, resulting from Mycoplasma pulmonis infection, is useful in the study of the immunological mechanisms in similar inflammatory diseases and provides a unique opportunity to study the interactions between systemic and mucosal immune systems in a naturally occurring infection. The present study examined the serum antibody responses to M. pulmonis in strains of rats which differ in disease progression and severity; LEW rats developed more severe disease than did F344 rats. Serum antibody responses were evaluated as to their levels, isotypes, and antigens recognized. Infected LEW rats produced greater or equal levels of the major classes of serum antibody to M. pulmonis than did infected F344 rats, suggesting that development of serum antibody responses alone does not resolve lesions and is not responsible for the difference in disease severity found in LEW and F344 rats. Although LEW rats produced higher responses in all subclasses of immunoglobulin G (IgG), the specific IgG response of LEW rats was composed predominately of IgG1 and IgG2a subclasses, while IgG2b was the major component of the IgG response in F344 rats. Finally, LEW rats responded more quickly to M. pulmonis antigens than did F344 rats, and there was no difference in the antigens eventually recognized by each strain, confirming previous work which suggested that LEW rats do not exhibit an unresponsiveness to a specific antigen(s) of M. pulmonis.

Short-term exposure to nitrogen dioxide enhances susceptibility to murine respiratory mycoplasmosis and decreases intrapulmonary killing of Mycoplasma pulmonis

In C57BL/6N and C3H/HeN mice known to be free of all murine pathogens and matched for age, sex, microbiologic, and environmental factors, exposure to NO2 for 4 h prior to exposure to infectious aerosols of Mycoplasma pulmonis resulted in potentiation of murine respiratory mycoplasmosis (MRM). In the C57BL/6N mice, NO2 increased the incidence of death, incidence of gross lung lesions, and incidence of microscopic lung lesions, but did not increase the incidence of infection in the lungs. Nitrogen dioxide affected the C3H/HeN mice (a strain known to be more susceptible than the C57BL/6N strain to MRM) similarly, with the exception that the incidence of death and microscopic lesions were not affected in this strain at the concentrations of M. pulmonis used. Exposure to the oxidant also increased the severity of microscopic lesions and the numbers of Mycoplasma organisms in the lungs of both mouse strains. Thus, NO2 appeared to affect host lung defense mechanisms responsible for limiting the extent of infection. The NO2 exposure level required to produce potentiation varied with the genetic background of the host, the number of Mycoplasma organisms administered, and the end point measured. In further experiments in C57BL/6N mice, exposure to 5 or 10 ppm of NO2 for 4 h prior to infection with aerosolized, radiolabeled M. pulmonis reduced clearance of these organisms from the lungs over a 72-h time period. Nitrogen dioxide exposure did not change the rate of physical removal of Mycoplasma organisms from the lung. Reduced clearance was due to impaired intrapulmonary killing of Mycoplasma organisms in NO2-exposed mice.(ABSTRACT TRUNCATED AT 250 WORDS)